The invention relates to a method of manufacturing a semiconductor device whereby a layer portion of a first layer is formed on a surface of a semiconductor body, the entire assembly is coated with a second layer from which an spacer is formed and with a masking layer which has a greater thickness next to the layer portion than above it, a treatment is carried out by which the etching resistance is increased in a portion of the second layer, at least in a top layer thereof, situated above the layer portion and the spacer to be formed, while next to the layer portion the masking layer acts as a mask against the treatment, and whereby the untreated portion of the second layer is selectively etched away relative to the treated portion so as to form the spacer.
Such a method, whereby an spacer is formed along the edge of the layer portion in a self-registering manner, is known from a Japanese Patent Application No. 61-129 832. According to the known method, after the masking layer has been provided, ions are implanted over the entire surface, for which such an energy is used that the ions penetrate through the masking layer above the layer portion and enter the top layer, whereas they remain in the masking layer next to the layer portion, where the masking layer is thicker. The undoped portion of the top layer is then etched away relative to the doped portion in trifluoromethane so as to form the etching mask.
A drawback of the known method, however, is that the masking photoresist layer must have a substantially equal thickness all over the layer portion for a satisfactory result, which is often not the case in practice. In many cases the photoresist layer will become gradually thinner from the centre to the edge of the layer portion. Moreover, the exact variation in the photoresist layer depends on a number of factors, among which the topography of the device, and is thus not well controlled. As a result of such thickness variations, it will often be impossible in practice to carry out the implantation in such a way that the ions end up mainly in the top layer everywhere above the layer portion, and in particular at the area of the spacer to be formed, in order to give the desired etching resistance to this top layer.